a. Field of the Invention
The present invention generally pertains to storage systems and more particularly to Redundant Array of Independent Disks (RAID) data storage systems as part of a Storage Area Network (SAN) system.
b. Description of the Background
A Redundant Array of Independent Disks (RAID) data storage system is a method of using multiple physical hard drives to act as a single logical hard drive for interaction with one or more host computers. A RAID storage device consists of an array of one or more hard disk drives controlled by a RAID controller. The RAID controller handles communication with external devices and coordination of the array operation for each of the individual hard disk drives. RAID systems are often used in mission critical jobs due to their flexibility in providing fast data access and hard disk drive fault tolerance.
A Storage Area Network (SAN) is a separate network for the special purpose of interconnecting multiple storage devices for use by one or more host data server computers. A SAN interconnects storage related resources and can be used to centralize data storage, thus providing a single addressing interface for multiple storage devices reducing the management costs and complexity of the data server computer environment. A SAN can incorporate many different types of data storage devices including Network-Attached Storage (NAS) devices and Direct-Attached Storage (DAS) devices. A NAS device is a standalone storage device, such as a RAID device, that connects directly to a Local Area Network (LAN) or Wide Area Network (WAN). A NAS device can be connected directly to the SAN system or incorporated as a sub-network of the SAN system. DAS devices, such as a Small Computer System Interface (SCSI) RAID device connected directly to a host computer data server. The SCSI connection between the RAID device and the host computer data server may be utilized as the SAN connection for the host computer data server. NAS devices typically support Internet Protocols (IP), such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) over Ethernet and other physical networking media. DAS devices typically support SCSI and Integrated Drive Electronics/Advanced Technology Attachment (IDE/ATA) communication protocols. A SCSI connection can be used to tie multiple storage devices into a SAN system with or without a direct connection to a host computer data server.
Fibre Channel (FC) is a newer technology protocol for storage devices, and is particularly suited to SAN systems. Fibre Channel is beginning to replace SCSI as the transmission interface between clustered data storage devices and host computer data servers. Fibre Channel is more flexible than SCSI and can be used with multiple physical media including optical fiber, ordinary telephone wire, coaxial cable, and other common networking physical media. In addition, Fibre Channel is designed to interoperate with SCSI, Internet Protocol (IP), and other protocols, giving direct connectivity to a wide variety of storage devices through the Fibre Channel connection. Information on the Fibre Channel protocol, and most other communication protocols, is kept by the American National Standards Institute (ANSI). ANSI is located at 11 West 42nd Street, 13th Floor, New York, N.Y. 10036, telephone number 212-642-4900, and web site www.ansi.org.
A Log-structured File System (LFS) writes all modifications to disk sequentially in a log-like structure, speeding up both file writing and crash recovery. A traditional file system lays out files near each other once on the disk drive. Thereafter, the files are rewritten over the original blocks whenever a change is made. In contrast, a log-structured file system always writes data blocks sequentially, so the write process always writes data that is next to each other on the disk drive without any intervening head seeks. The log is the only structure on the disk. The log contains indexing information so that files can be read back from the log efficiently.